1. Field of the Invention
The present invention relates to a method of manufacturing a commutator for electric rotary machines mounted in an automotive vehicle.
2. Description of the Prior Art
A conventional method of manufacturing a commutator, for example, as exemplified in U.S. Pat. No. 3,423,819, comprises substantially the following steps; first, the copper metal is formed into a generally circular configuration desired for the elongated commutator blank, with one end of the length of the metal positioned adjacent the other end of the length of the metal in parallel, spaced relationship therebetween; second, the copper metal in the area adjacent the two ends of the length is subjected to an electron beam welding operation so as to form a welded joint between the two ends; third, the copper metal formed to a continuous and circular commutator blank is annealed so as to relieve all stresses and strains developed therein during both the forming and electron beam welding steps; fourth, the commutator blank is immersed in a soap solution for the subsequent extrusion operation; fifth, the commutator blank is extruded to form a segment ring having bridging portions formed across gaps between commutator segments and flanged portion for connecting armature windings; sixth, holding claws are provided on inner surfaces of the commutator segments; seventh, the segment ring is molded with an insulating material; eighth, the outer surface of the segment ring is cut to remove the bridging portions thereby to divide the segment ring into individual segments.
The above described method of making the commutator, however, has disadvantages that the electron beam welding step must be carried out in a vacuum furnace which results in a batch processing or a lot production, whereby commercial quantity production is hardly achieved, that the vacuum furnace requires a large-scale vacuum pump and electric equipment to supply a high voltage, and that large-scale equipment for heat-treatment is required to form homogeneous metallographical properties.